The present invention relates to a method for determining a model of flowrate through a valve.
A particular application relates to a valve delivering a flowrate toward an intake manifold of an internal combustion engine. Still more particularly, the invention may be applied to a canister purge valve.
The context is that of the environment of an intake manifold as shown in the diagram of FIG. 1. This diagram depicts an internal combustion engine 5. This engine 5 comprises an intake manifold 9, for introducing air into the engine 5 to enable the combustion of a fuel to take place therein, and an exhaust 11 for discharging the combustion products.
The fuel is typically a liquid in the form of a volatile mixture of hydrocarbons, the vapors of which are polluting. To prevent pollution of the external environment, the fuel is stored in a liquid-tight and gas-tight tank 3. In order to accommodate the inevitable variations of pressure in the tank 3, the latter is connected, via a line 13, to a filter or canister 2 capable of capturing the vapors emitted from the fuel, while letting air escape via a kind of vent outlet 12, to allow the pressure to decrease. This canister 2 comprises a volume filled with an absorbent material such as activated carbon. The volume of this absorbent material gives the canister 2 a specific vapor capture and storage capacity. To regenerate this capacity, the canister 2 is advantageously purged, said vapors stored in the canister 2 being sent toward the engine 5 to be burnt there. This is done by means of a purge valve 1, connected to the canister 2 by a line 14 and to the intake manifold 9 by a line 15. When the purge valve 1 is open, suction of the vapors stored in the canister 2 is provided by a pressure drop created by the engine 5.
As shown in FIG. 1, an engine control unit 4 controls, in a conventional and known way, a reduced area controller 6 which regulates the flowrate of air admitted into the intake manifold 9 and consequently into the engine 5. The engine control unit 4 receives information from the richness sensor 7, and controls the purge valve 1, together with the injector(s) 8, to manage the purging of the canister 2 while maintaining a stoichiometric mixture in the cylinders.
A first problem is that of estimating the load, or utilization of capacity, of the canister 2, for the purpose of determining an optimal purge strategy based on the operating phases of the engine, on the one hand, and estimating the contribution of the canister 2 to the fuel supply to the engine 5 on the other hand, in order to reduce the contribution of the normal fuel supply circuit by the same amount, typically by means of one or more injectors 8.
The estimation of the load of the canister 2 is covered by another patent application filed by the present applicant. The principle is that of opening the purge valve 1 and observing the result of this opening on the deviation of a richness sensor 7 positioned in the exhaust 11. Said deviation is representative of an amount of fuel that has left the canister 2. The load of the canister 2 is estimated as a function of this amount related to the flowrate through the purge valve 1 during its opening.
Thus the estimation of the canister load requires precise modeling of the flowrate through the purge valve 1 as a function of the applied opening command. Other applications may require the knowledge of a flowrate model.
In order to be able to use a valve 1 appropriately, it is necessary to know the flowrate D through the valve 1 as a function of a command C applied to the valve 1. For this purpose, a model M may be used in order to relate a flowrate D to a command C applied to the valve 1. This model M may take different forms. It relates a flowrate value D to a command value C, or vice versa. It may be a function, D=FM(C) or C=GM(D), or alternatively a table of points (C, D). Such a model, generically denoted M, has a characteristic curve, of which three examples M0, M1, M2 are shown in FIG. 2, according to a diagram representing the command C on the horizontal axis and the flowrate D on the vertical axis. This characteristic curve M, M0, M1, M2 typically comprises three parts, namely a first, substantially horizontal, part between the origin 0 and an opening point P0, where, as long as the command C remains below a threshold value, the valve 1 remains closed and no flowrate is present (D=0); a second part, between the opening point P0 and a point Pmax, where the flowrate D varies between 0 and a flowrate substantially equal to a maximum flowrate Dmax of the valve 1, as the command C increases; and a third part, beyond the point Pmax, which is substantially horizontal, where the flowrate is substantially equal to the maximum flowrate Dmax, independently of the further increase in the command C.
One difficulty is that of estimating the position of the opening point P0, P0′. Another patent application filed by the present applicant proposes a solution to this problem. Reference may usefully be made to this. The opening point P0, P0′ may also be determined by the identification of the valve 1 on a test bench. The opening point P0, P0′ is assumed to be known in the remainder of the present description.
The characteristic curve M0, shown in solid lines, represents a “nominal” or average valve. However, it appears that valves used in practice may exhibit “deformed” characteristic curves, such as the characteristic curve M1, shown in the dotted line, or the characteristic curve M2, shown in the dashed line. Such variations may thus appear within the same series of valves, due to manufacturing variations (in terms of material, dimensions, supplier, etc.). These variations, relative to a “nominal” model, as illustrated by the characteristic curve M0, are so disturbing for the intended uses, such as canister load estimation, that they must be taken into account.
There is a known document US 2014/116526 which relates to an EGR valve controller. The method includes estimation of the flowrate through the valve, which is carried out with the use of a position sensor integrated with the EGR valve and an external measurement of the flowrate through this valve at the end of the production line in the manufacture of this valve. According to this document, a valve position sensor is necessary for the estimation of the flowrate.
The object of the invention is to determine a flowrate model M which associates a flowrate D with a command C for a valve 1.